OKLAHOMA CITY (AP)  A judge must decide if a man accused of beheading a co-worker at a food processing plant in suburban Oklahoma City is competent to contribute to his own defense on a first-degree murder charge.

Alton Nolen, 31, is charged in the knife attack at Vaughan Foods in Moore in September last year that killed his 54-year-old co-worker Colleen Hufford. Nolen is also charged with assault and battery with a deadly weapon in an attack on a second colleague, 43-year-old Traci Johnson, who survived.

He has pleaded not guilty to both charges. Prosecutors are seeking the death penalty.

Cleveland County District Judge Lori Walkley cannot set a trial date until she has determined whether Nolen has the mental capacity to participate in a trial.

To be convicted of a crime, federal law requires that a defendant is able to consult with his lawyer and understand the nature of the legal proceedings against him. Nolen’s defense attorneys claim he is unable to help them prepare his defense and thus should not stand trial.

A rare non-jury competency trial is scheduled to begin Monday and could take up to three days. District Attorney Greg Mashburn said the competency trial will include psychological testimony from witnesses for both sides.

Joseph Thai, a professor at the University of Oklahoma College of Law, says determining a defendant’s competence for trial is different from determining whether a defendant was insane at the time of the offense.

“Due process guarantees a fair trial, and a trial cannot be fair if the accused is incapable of assisting in his own defense,” Thai said.

Psychological examinations of Nolen have been filed under seal in the case and defense attorneys have not said whether they plan to pursue an insanity defense if the case goes to trial.

Investigators said Nolen had just been suspended from Vaughan Foods when he walked into the company’s administrative office and attacked Hufford with a large knife, severing her head. He then repeatedly stabbed Johnson before he was shot by Mark Vaughan, a reserve sheriff’s deputy and the company’s chief operating officer.

Authorities have said Nolen had recently converted to Islam and apparently uttered Arabic words during the attack. Mashburn has said Nolen had “some sort of infatuation with beheadings,” but that the attack appeared to have more to do with his suspension than his religious conversion.